Spinal fusion is a procedure that involves joining two or more adjacent vertebrae with a bone fixation device to restrict movement of the vertebra with respect to one another. For a number of known reasons, spinal fixation devices are used in spine surgery to align and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as, for example, a relatively rigid fixation rod, a dynamic or flexible spinal rod, etc., that is coupled to adjacent vertebrae by attaching the spinal fixation element to various bone fixation elements, such as, for example, hooks, bolts, wires, screws, etc. The bone fixation elements may commonly include heads with channels in which the spinal fixation element is inserted and subsequently clamped by a set screw or closure cap. Surgeons may commonly choose to install multiple bone fixation elements, as well as multiple spinal fixation elements, to treat a given spinal disorder. The spinal fixation elements may have a predetermined contour, and once installed, the spinal fixation element may hold the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
Surgeons have often encountered difficulty installing such devices because of trouble aligning the spinal fixation element(s) with the channels in the heads of the bone fixation elements. For example, the heads of bone fixation elements may often be out of vertical and/or horizontal alignment with one another because of the curvature of the spine or the size and shape of each vertebra.
The process of positioning and setting known bone fixation elements may be tedious and relatively time-consuming, typically requiring more than one surgical tool to clamp the spinal fixation elements and the bone fixation elements in desired positions. Even with a high degree of skill and care, the process of positioning an assembly of known bone fixation elements and spinal fixation elements, and clamping said bone and spinal fixation elements in place can take more time than desired during a surgical procedure, and may even result in spinal fixation elements, bone fixation elements, or both moving out of position before clamping is completed.
Thus, it is desirable to have a spinal fixation device that can secure spinal fixation elements and bone fixation elements in place with a minimum amount of time and a minimal number of surgical tools. It is also desirable to have a spinal fixation device that can secure a spinal fixation element at an axis that is offset from the axis of the bone fixation element.